As shown in FIG. 1, each pixel unit 1 of an organic light emitting diode (OLED) display device (i.e., a “dot” on the display screen) consists of a plurality of adjacent sub-pixels 8 in a same line, while each sub-pixel 8 includes one light emitting diode (LED). various sub-pixels 8 emit light of different colors (for example, in RGB mode, each pixel unit 1 consists of three sub-pixels R, G and B emitting red, green and blue light). To allow sub-pixels 8 to emit light of different colors, one way is to make all sub-pixels 8 of an OLED to emit white light and filters of different colors are disposed in sub-pixels 8 for filtering at the same time; however, a more typical method is to use different organic light emitting layer materials in organic light emitting diodes of different sub-pixels 8, allowing the organic light emitting diodes to emit light of different colors directly.
For an OLED display device using different organic light emitting layer materials for various sub-pixels 8, it is understood that organic light emitting layers of sub-pixels 8 of different colors need to be manufactured separately in different evaporation processes (however, other structures such as electrodes in sub-pixels 8 may be formed at the same time). As shown in FIG. 1, when evaporating an organic light emitting layer of a sub-pixel 8 of a certain color, a barrier section 91 of the evaporation mask 9 (FFM) is used to shield other sub-pixels 8, so as to allow the organic light emitting layer material to be deposited on the desired sub-pixel 8 via an opening 92 (in the column direction, sub-pixels 8 of the same color are aligned in one column, and their organic light emitting layers are connected together, thus no barrier section 91 is needed).
As shown in FIG. 2, the barrier section 91 has a width c=(b+2d×tan α), wherein b is a width of the middle part of the barrier section 91, d is the thickness of the evaporation mask 9 and α is the slope angle of the barrier section 91. In order to guarantee a good shielding effect, α of the evaporation mask 9 is generally kept at 40˜60 degrees. At the same time, due to the limitations of the conventional manufacturing process, it is difficult to obtain d less than 30 μm. Therefore the minimum value of the width of the barrier section 91 is also limited. Since the width of the barrier section 91 is the space between sub-pixels 8 of the same color (for RGB mode, it is the width of two sub-pixels 8), limitation on minimum width of the barrier section 91 is equivalent to the limitation on minimum size of the sub-pixel 8, resulting in limitation on resolution (the number of pixel units 1 per unit size), and hence impacting on the display quality.
In order to improve the resolution of an OLED display device, a Pentile arrangement of sub-pixels 8 has been developed. In the Pentile arrangement, as shown in FIG. 3, the number of red and blue sub-pixels R and B is reduced by one half, and every red and blue sub-pixel R, B is “shared” by two pixel units 1. As such, it is possible to increase the number of pixel units 1 and enhance to increase the resolution while keeping the number of the sub-pixels 8 unchanged. Obviously, in the Pentile arrangement, the number of part of the sub-pixels 8 (such as red and blue sub-pixels R, B) is reduced and the shared sub-pixels 8 can not display contents of two pixel units 1 accurately at the same time, it is necessary to adjust areas of some sub-pixels 8 (for example, enlarge areas of red and blue sub-pixels R and B) incorporating with certain display algorithms (i.e., algorithms for calculating gray-scales of sub-pixels 8) to guarantee that the display quality is not degraded.
The inventor notices at least the following problems in conventional technology: the size of sub-pixels in Pentile arrangement is stilled limited by the barrier area width of the evaporation mask, and the size of sub-pixels is not decreased (some even get larger), that is, this arrangement cannot improve the resolution of an OLED display device essentially.